1. Technical Field
The present invention relates to a printing apparatus that prints an image or the like by ejecting liquid on a printing medium.
2. Related Art
An ink jet printer having one printing apparatus forms micro ink dots on a printing medium by ejecting (spraying) liquid ink droplets from nozzles of a liquid ejecting head (sometimes, referred to as an “ink jet head”) so that an image or the like is printed. As an example of the ink jet printer, there is a multi-pass type ink jet printer where the ink jet head is mounted on a moving body referred to as a carriage to be moved in a direction intersecting a transport direction of the printing medium. In addition, in another example of the ink jet printer, there is a line head type ink jet printer where printing is performed by an ink jet head that is elongated (not necessarily integrally provided) in the direction intersecting the transport direction of the printing medium (that is, so-called one-pass printing can be performed).
In such an ink jet printer, a process of heating the printing medium is performed so as to dry and fix the printed ink on the printing medium. Various types of printing medium heating units for the printing apparatuses have been proposed. For example, in a printing apparatus disclosed in JP-A-3-251474, a heating plate unit for heating the printing medium along the transport path of the printing medium is provided. In addition, in the printing apparatus, the printing medium is heated to have a preliminary heat before the printing, the printing medium is heated at a temperature lower than the preliminarily heating temperature during the printing, and the printing medium is heated at a high temperature to rapidly dry the ink after the printing.
However, like the printing apparatus disclosed in the JP-A-3-251474, in a case where the heating temperature during the printing on the printing medium is designed to be lower than the heating temperatures before and after the printing, the temperature of the printing medium at the time of the preliminary heating is designed to be high in order to dry the ink. In addition, when the printing medium in the preliminarily heated state is contacted and transported by a PF (paper feed) roller having no heater, the temperature of the printing medium is decreased. After that, every time when the printing on the printing medium is continuously repeated, the temperature of the PF roller is increased, so that the temperature of the printing medium is also increased. Therefore, the temperature of the printing medium during the printing cannot be maintained at a constant level. As a result, the ink absorption capability of the printing medium is varied with the printing, so that concentration non-uniformity, color non-uniformity, or the like may occur. Therefore, uniformity of image quality may not be secured.